A GPS (Global Positioning System) is conventionally known as a scheme for estimating its position when mounted in an automobile or other moving object. According to the GPS, its position can be estimated when signals transmitted from a predetermined number of satellites are received. However, if, for example, the GPS is traveling near a high building or through a tunnel, the position of the GPS cannot be estimated because the above-mentioned signals cannot be received.
If such inconveniences are caused so that the position of a moving object cannot be estimated, the subsequent movement (the direction and speed of movement) of the moving object (e.g., an automobile) should be continuously detected with a known location at a certain time point defined as a reference point. More specifically, for example, a conceivable method is to mount a camera on the moving object, continuously capture an image of surroundings to obtain chronological images, and detect the movement of the moving object in accordance with the movement of a same subject in the chronological images.
However, if the employed method detects the movement of the moving object in accordance with the captured images of the surroundings, an inconvenience may arise. More specifically, the movement of the moving object cannot readily be continuously detected if the captured images show blown-out highlights due to ambient light, are mostly occupied by another moving object (e.g., a preceding large-sized automobile) that travels together with the own moving object, are unclear due to heavy rain or other bad weather, or merely show a distant view due to the absence of an appropriate nearby subject.
A method proposed to address the above problem is to detect the movement not by capturing the images of the surroundings of the moving object, but by tracking feature points on a road surface that are represented in chronological images obtained by continuously capturing the road surface (refer, for example, PTL 1 or 2).
Note that, in order to detect the movement by tracking feature points on a road surface, it is necessary to accurately measure the distance between the road surface and the camera (the height from the road surface to the camera). According to PTL 1, two laser pointers project reference marks onto a road surface in order to measure the road surface-to-camera distance in accordance with the distance between the reference marks. According to PTL 2, the road surface is irradiated with a light beam in a square lattice pattern in order to measure the road surface-to-camera distance in accordance with the distortion of the square lattice pattern.